180 Anatomy of the Rabbit. 



Examine the following muscles, proceeding in a similar manner: 



(a) The internal oblique muscle (m. obliquus interims 

 abdominis). Origin: The inguinal ligament, a second sheet 

 of the lumbodorsal fascia, and the posterior four ribs. 

 Insertion: The linea alba. The fibres pass downward and 

 forward. The ventral aponeurosis is much broader than 

 that of the external oblique. It contains the rectus ab- 

 dominis. 



(b) The transverse muscle (m. transversus abdominis). 

 Origin: Seven posterior ribs, a third sheet of the lumbo- 

 dorsal fascia, and the inguinal ligament. Insertion: The 

 linea alba. The fibres are directed downward and slightly 

 backward. 



(c) The rectus abdominis muscle. Origin: Lateral border 

 of the sternum, including the xiphoid, process; also the 

 ventral surfaces of the second to seventh costal cartilages. 

 Insertion: At the anterior end of the pubic symphysis. It 

 is a thin, strap-like muscle, enclosed by the aponeurosis 

 of the internal oblique, and separated from its fellow of the 

 opposite side by the linea alba. 



The artery passing forward, for the most part in this muscle, is the 

 inferior epigastric, a branch of the external iliac (p. 203). It anastomoses 

 with the internal mammary (p. 257). It gives off the external spermatic 

 artery, a small vessel which perforates the abdominal wall and extends 

 backward, supplying the sac of the testis in the male and ending in the 

 female in the wall of the vulva. 



5. Divide the remaining portion of the wall on the left side, and 

 its whole thickness on the right, by a transverse incision, so that 

 the viscera are fully exposed. Note on the internal surface of 

 the wall the smooth serous investment here forming the parietal 

 peritoneum (peritonaeum parietale). 



